The parasternal long-axis view allows for visual assessment of mitral valve morphology and leaflet excursion. It demonstrates A2 and P2 scallops. Leaflet motion and thickness and the presence and extend of calcification should be reported. The characteristic doming of the anterior leaflet is better seen in this view (Figure 1). In mitral stenosis, color Doppler demonstrates diastolic turbulence across the mitral valve in this view.

The parasternal short-axis view allows for visual assessment of the leaflets and commissures. Commissural fusion is best seen in this view. The posteromedial (left) and anterolateral (right) commissures are visualized. Scallops one to three are seen from the anterolateral commissure to posteromedial commissure. This view is also used to perform planimetry of the mitral leaflet tips. Tilting from base to apex will demonstrate the narrowest valve orifice (Figure 2).

The apical four chamber view typically demonstrates A3, A2, and P1 scallops from left to right (Figure 3A). It allows for visual assessment of the anatomy and mobility of both mitral leaflet. Continuous wave Doppler parallel to the mitral inflow in this view is used to measure transmitral gradients across the valve (Figure 3B). The densest portion of the curve should be used. Calculation of mitral valve area by PHT is also performed in this view (Figure 3C).

Table 1 shows the classification of mitral stenosis severity according to mitral valve area and supportive findings.

Suitability of mitral valve for percutaneous mitral commissurotomy is based on echocardiographic findings. Scoring systems have been developed to help with this task. The Wilkins score [17] (Table 2) is the most widely accepted criteria for patient selection.

Percutaneous mitral commissurotomy is contraindicated in patients with a mitral valve area >1.5cm², left atrial thrombus, more than mild mitral regurgitation, severe calcification, absence of commissural fusion, severe concomitant aortic valve disease, severe combined tricuspid stenosis and tricuspid regurgitation requiring surgery or concomitant coronary artery disease requiring surgery [4].

Biplane mode allows for the use of a dual screen to display the mitral valve in two planes in real time. The second plane is usually orthogonal, though any rotation angle can be used. Color Doppler imaging can also be used together with biplane imaging. This mode is useful for a preliminary evaluation of the mitral valve. Scallops and segments of the mitral valve can be investigated by manipulating the lateral plane in different angle orientations in order to provide detailed information regarding mitral valve anatomy and the mechanism and etiology of mitral stenosis. In transthoracic echocardiography, biplane imaging can help ensure that planimetry takes place at the leaflet tips. An orthogonal plane can be obtained placing the cursor at the leaflet tips in the parasternal long-axis view. However, in order to avoid an oblique short-axis view, adequate alignment of the mitral orifice in the long-axis view is required.

Full volume imaging provides the largest sector and allows for an evaluation of the entire mitral valve apparatus. Real-time full volume acquisitions generally result in poor spatial and temporal resolution. Therefore, whenever possible, ECG gating acquisitions should be used. A full volume with gated acquisition is reconstructed by merging several individual volume slices gated to the ECG. This results in high temporal and spatial resolution. However, it can also be susceptible to artefacts due to arrhythmias and/or respiratory motions. ECG should be optimized to show a distinct R wave and the number of acquisition beats should be adjusted attending to the patient’s circumstances. Moreover, images should be obtained with breath-holding. Once acquired, the full volume dataset can be cropped, rotated, viewed in multiple perspectives, or decomposed into 2D cross-sections.

Real-time 3D imaging permits a narrow sector and therefore higher spatial and temporal resolution. However, the sector is generally insufficient to visualize the entire mitral valve apparatus. The pyramidal volume should be acquired at a decreased depth and focused on the mitral valve. This allows for an initial 3D evaluation of the mitral valve.

Focused wide-sector imaging allows for a 3D focused view of the mitral valve. In transthoracic echocardiography, 3D zoom of the mitral valve can be acquired from both the parasternal and the apical views (Figure 5). The anterior leaflet is adequately visualized in both views while the posterior leaflet is better seen from the parasternal view [18]. The mitral valve should be oriented with the aortic valve placed superiorly regardless of if the valve is oriented as viewed from the left atrium or the left ventricle (Figure 6) [19].

Three-dimensional echocardiography is superior in evaluating mitral stenosis severity, because direct visualization of the valve orifice in multiple planes ensures that the planimetry takes place at the level of the mitral leaflet tips, where the valve orifice is narrowest. Indeed, 3D planimetry has been reported as the most accurate method for mitral valve area evaluation [20,21], and it has become the reference method for mitral valve area quantification.

In order to perform 3D planimetry, the 3D zoom dataset should include the entire mitral annulus and the leaflet height. Later, the frame when leaflet excursion is greater should be identified and multiplane reconstruction should be used to achieve a parallel alignment with the narrowest portion of the mitral valve orifice. Finally, the mitral valve area is obtained tracing the inner edge of the orifice (Figure 7). Modern software permits multiple short-axis slices to be reconstructed to help identify the narrowest mitral valve orifice (Figure 8).

A scoring system based on 3D echocardiography, the Anwar score, has been developed for the evaluation of patients before percutaneous mitral commissurotomy [22] (Table 3).